1. Technical Field
The present invention relates to controlling a disk drive and, in particular to a system and method for stabilizing rotation control for a hard disk drive (HDD). More particularly, the present invention relates to a disk drive control system suitable for dynamically adjusting a slew of a HDD servo motor current such that a rotation control of a servo motor driving a storage disk is stabilized during periods of varying servo motor load.
2. Description of the Related Art
During operation a disk drive, a disk storage medium such as a magnetic disk rotates at high speeds thus creating an air bearing (a thin cushion of air) on which a head slider xe2x80x9cflies.xe2x80x9d The head slider is mounted on a suspension assembly constituting a head arm of an actuator mechanism, and is floated off the disk surface from which the head writes or reads out data to or from the storage medium. For one type of HDD, during non-activated periods in which rotation of the storage medium is stopped, the head slider lands on a landing zone on the disk surface. The landing zone is typically an area on the storage medium where no data is recorded. Such a disk drive is referred to as a contact-start-stop type disk drive.
In the aforementioned contact-start-stop type disk drive, there is a possibility that adhesion of the head slider to the surface of the data area or movement of the head slider to the data area due to shock will cause scoring and galling of the disk surface. A type of HDD that is designed to avoid such a problem is called a load/unload HDD. The load/unload type disk drive is equipped with a specialized loading/unloading mechanism. The loading/unloading mechanism includes a head holding mechanism that comprises a suspension assembly for a head arm, and a component called a ramp block that is included within the disk drive.
During periods of non-activation of the disk drive, the loading/unloading mechanism unloads the head slider to a predetermined xe2x80x9csave positionxe2x80x9d on a ramp block such that that the slider avoids contact with the disk surface. This is accomplished by holding the suspension assembly at the save position on the ramp block. The aforementioned suspension assembly is provided with a tab having a protruding portion, and the aforementioned ramp block is provided with a ramp. The ramp block is disposed so that the ramp is located near the outer circumference of the disk. Upon deactivation of the disk drive, the loading/unloading mechanism unloads the head slider by retracting the head arm toward the ramp block and placing the protruding portion of the tab of the suspension assembly on the tab-holding flat surface of the ramp.
Upon activation of a load/unload type disk drive, the head is loaded after the rotation of the storage medium has become stable. This stability is achieved when a motor that rotates the storage medium has achieved an electrical steady state after being started. The determination of rotation stability requires recognizing the point in time at which the loading coincides synchronously with servo information written to the storage medium (called servolock).
For disk drives in which the rotational speed of the storage medium is 10,000 rpm or greater, and furthermore, for disk drives having a large number of storage media and heads, the head sliders will be subjected to air resistance as soon as they are loaded to the storage media, and consequently, the rotation load on the aforementioned motor will rise abruptly. Without compensation for this abrupt rise in load, the rotational speed of the aforementioned motor will decrease abruptly. A control band is normally provided for providing stable rotation control with respect to an abrupt increase in current.
To achieve the aforementioned control band, a disk drive utilizes a three-phase DC servomotor. with respect to a three-phase DC servomotor, two of three coils conduct, that is, two phases become conducting phases, and the remaining phase is non-conducting, or xe2x80x9coffxe2x80x9d. When a back electromotive force is detected in the OFF phase,xe2x80x94the conducting phase is switched. A sharp current change occurs when the conducting phase is switched, resulting in additional operating noise from the motor. To solve this problem, a current slew rate is adjusted so that a rise and a fall in the phase current is less pronounced when the phase current is switched. However, if such a current slew rate adjustment is performed in the absence of an actual shift in current, while the detection of a back electromotive force can be performed accurately, the time during which current does not flow with respect to the OFF phase is shortened, resulting in a current flow with respect to the OFF phase, i.e., xe2x80x9ckick backxe2x80x9d that occurs as soon as current changes. For a load/unload type disk drive, this xe2x80x9ckick backxe2x80x9d will increase and a back electromotive force will be detected at incorrect timing, because a sharp increase in current becomes necessary if the head slider is loaded to the storage medium, as described supra. As a consequence, it becomes difficult to precisely control rotation of the aforementioned motor.
From the foregoing it can be appreciated that a need exists for a system and method that ensures stable rotation control of a disk drive servo motor during periods of abrupt load fluctuations.
A system and method for providing rotation control stability within a disk drive are disclosed herein. In accordance with the system of the present invention, a disk storage medium on which information is recorded is driven to rotate by a multiphase-phase DC servomotor. An actuator is utilized for loading and unloading the head to and from the disk storage medium. A load/unload controller commands the actuator to load or unload said head. In order to effectively compensate for an abrupt change in load on the servomotor caused by loading the head onto the disk storage medium, a slew rate switching unit is utilized to alter a slew rate of current supplied to the three-phase DC servomotor, based on a loading start command issued by the load/unload controller.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.